Fabrics that are impregnated or coated with resins, especially polyurethane resin, are used in artificial leathers. Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, John Wiley & Sons, Inc., Volume 15, “Leather-like Materials” p. 177–192, (1995) summarizes the development of such materials. The encyclopedia notes that in the 1930s, a plasticized poly(vinylchloride) film coated onto a woven or knitted fabric was developed as a leather-like material, but the material was stiff, exhibited plasticizer migration and had extremely low permeability, poor flex endurance and a cold touch. In the 1960s, synthetic leather materials having improved appearance, feel and resistance to grain breakage were made by laminating a cast polyurethane film to a brushed fabric. Further improvements in flexibility were achieved with the introduction of poromeric polyurethane-coated fabrics which were produced by applying a solution of a polyurethane resin in an organic solvent to a brushed fabric and then immersing the fabric in a non-solvent bath (e.g., water) to coagulate the polyurethane and form the poromeric structure. Typically, a cast polyurethane film was applied atop the poromeric structure. Polyurethane-impregnated and coated nonwoven fabrics made with ultra-fine fibers or microfibers (i.e., of less than 0.3 denier) also were developed to produce suede-like and other leather goods.
Combinations of various woven or knitted fabrics with nonwoven materials also have been disclosed for use in making artificial leather. For example, U.S. Pat. No. 5,256,429, entitled “Composite Sheet for Artificial Leather,” to Honda et al, discloses making a composite sheet by needle punching a surface layer of special staple fibers of very low denier into a tightly woven or tightly knit fabric of high twist multifilament yam and then coating or impregnating the resulting structure with a binder. The special fibers are formed from “islands-in a-sea” composite fibers by dissolving the polymeric “sea” surrounding “islands” of a second polymer to leave fibers of very low titre (i.e., 0.001 to 0.1 denier). However, making artificial leather products from “islands-in-a-sea” fibers is costly.
U.S. Pat. No. 4,073,988, entitled “Suede-like Artificial Leathers and a Method for Manufacturing Same,” to Neshida et al, discloses an artificial suede leather made from pile-like fibers by subjecting the fibers to a heat treatment and a swelling treatment before impregnating or coating the fibers with a synthetic polymer solution or emulsion. The solution or emulsion is then coagulated, and dried. The sheet is then buffed to raise naps. The filaments making up the pile-like fibers have complex cross-sections, created by bonding different polymers having mutually low adhesive affinity with each other. The artificial leather disclosed in '988 patent has only one surface that displays the leather-like appearance, while the other surface shows the fibers of the composite. This appearance reduces the appeal of artificial leather. Furthermore, an additional buffing step is required to produce raised naps.
U.S. Pat. No. 4,329,390, entitled “Method for Making Leatherlike Materials (B),” to Civardi et al discloses a synthetic leather-like sheet made from laminating a thin micro-porous elastomeric layer, a fibrous backing and a very thin preformed skin. The thin preformed skin is embossed to create a grain appearance. Again, this synthetic leather sheet only resembles leather on one surface.
U.S. Pat. No. 5,922,445, entitled “Composite Material and Process for Production of Same,” to Yoshida et al discloses another leather-like composite sheet. The composite sheet is obtained by coating or impregnating a fibrous base material with an elastic polymeric substance, in which the fibers constituting the fibrous base material and the elastic polymeric substance are prevented from bonding with each other. This sheet may be produced by applying a hydrophobicizing treatment to the fibrous base material, then impregnating or coating a solution of the elastic polymeric substance to which a hydrophilic silicone has been added, and wet solidifying. Similarly, this synthetic leather composite sheet only resembles leather on one surface.
Recent advances in stitch-bonded composites suitable for use as artificial leather are disclosed in U.S. Pat. No. 5,707,710, entitled “Composite Sheet for Artificial Leather” to Zafiroglu, U.S. Pat. No. 6,063,473, entitled “Abrasion-Resistant Composite Sheet” also to Zafiroglu and U.S. Pat. No. 6,407,018 B1 (col. 5, 1. 47 to col. 6, 1. 13), entitled “Stitchbonded Fabric and Process for Making Same” to Zafiroglu. While these composites function well, the overlap yarns from the technical front and/or the underlap yarns from the technical back remain visible to the unaided eyes, as shown in FIGS. 1 and 2. Additionally, conventional composites can also have a rough or bumpy appearance that requires a post-processing brushing step to provide a more desirable combed or napped surface.
Hence, there remains a need in the art for artificial leather that in addition to having leather-like qualities also has an appearance that is closer to authentic leather.